(1) Field of the Invention
The present invention relates to a playback apparatus and a playback method for rights protected content, and a recording medium on which data used in the playback apparatus and playback method is recorded.
(2) Prior Art
CSS (Content Scrambling System) has been introduced into DVDs (Digital Versatile Discs) in order to prevent illegal copying of content. In CSS, information unique to the DVD medium is recorded on the DVD medium, and a title key is generated from the unique information and information held by a playback apparatus. The title key generated in this way is used to decrypt, and then playback, the encrypted content recorded on the DVD medium (see Japanese Laid-Open Patent Application No. 2003-37589).
Meanwhile, content distribution systems that use DRM (digital rights management) are starting to become common in recent years. In DRM, a license is distributed separately to the encrypted content. The license includes a license key and usage conditions, and the playback apparatus decrypts and plays back the content with the license key, in accordance with the usage conditions.
In DRM, the content and license are distributed via a network. Furthermore, tests are being performed recently for distributing content in a storage-type broadcast system called server-type broadcasting.
BDs (Blu-ray Discs) are a type of medium that has been proposed for use instead of DVDs. A BD has approximately five times the capacity of a DVD, and is capable of storing not only SD picture quality video as has been possible up to now, but also HD picture quality video.
Similar to CSS in conventional DVDs, BDs use a system in which information unique to the medium is recorded on the BD, and a medium key is generated from this information and information held by the playback device. The medium key obtained in this way is used to encrypt the content, and the encrypted content is recorded on the medium. This kind of method prevents illegal copying of the content in the same manner as with DVDs.
Furthermore, ways of applying DRM to BDs are being investigated. When DRM is applied to packaged media, content that has been encrypted with a license key is stored on the medium, and the license is distributed separately over a network. At the time of playback, the encrypted content recorded on the medium is decrypted with the license key and played back.
However, when applying DRM to BDs, a problem arises when both content that is copy protected in a conventional manner and content to which DRM is applied exist on the medium. In such a case, the player is unable to distinguish between content that is copy protect in a conventional manner and content to which DRM is applied. If the player attempts to use the medium key to decrypt content to which DRM is applied, the player will be unable to decrypt the content. Conversely, if the player attempts to search for the license that corresponds to the content that is copy protected in a conventional manner, the player will not be able to play the content back because no corresponding license exists.